rvt-rs

Apache-2.0 clean-room Rust/Python toolkit for inspecting Autodesk Revit files (.rvt, .rfa, .rte, .rft) without a Revit installation. Opens the OLE/CFB container, decodes Revit's truncated-gzip streams, extracts metadata and previews, parses the embedded Formats/Latest schema, and classifies all observed schema field encodings across an 11-release 2016–2026 reference corpus.

This is not yet a full Revit model reader. Schema-directed instance walking has a verified ADocument beachhead on Revit 2024–2026, 80 per-class decoders registered in elements::all_decoders() (Wall, Floor, Door, Window, Column, Beam, Stair, Railing, Rebar, Room/Area/Space, Furniture, DesignOption, Phase, Workset, and many more), and IFC4 STEP emission that produces a valid spatial tree with per-element entities, rectangular geometry, compound-layer materials, typed property sets, and door/window openings. Real-world project-file corpus validation (Q-01) is active research — the shipped 11-release test corpus is family-scale (.rfa); one .rvt project probe already surfaced and fixed a latent bounds bug in gzip_header_len. See What works today for the precise boundary.

A zero-upload, client-side browser viewer ships alongside the library, live at https://drunkonjava.github.io/rvt-rs/. Drop a .rvt / .rfa file onto the page — the WebAssembly build parses it in-tab, renders 3D via Three.js with orbit controls + element picking + scene tree, and offers one-click Export glTF / Export IFC / Export plan SVG. No upload, no account, no telemetry. CI asserts the compiled .wasm has zero fetch / XMLHttpRequest / WebSocket imports.

Rust 2024 edition (MSRV 1.85). Fourteen CLIs ship (rvt-analyze, rvt-info, rvt-schema, rvt-history, rvt-diff, rvt-corpus, rvt-dump, rvt-doc, rvt-ifc, rvt-write, rvt-gltf, rvt-sheet, rvt-elem-table, gen-fixture) plus 36 reproducible probes under examples/. Python bindings via pyo3+maturin in the rvt-py workspace member (SEC-12/13 — the core rvt crate is unconditionally #![forbid(unsafe_code)]) — pip install rvt.

What works today

Layer	Status	Notes
OLE/CFB container open	✓	No Revit required
Truncated-gzip stream decode	✓
BasicFileInfo metadata	✓	Version, build, GUID, original path
PartAtom XML	✓	Title, OmniClass code, taxonomies
Stream preview extraction	✓	Clean PNG, wrapper stripped
Formats/Latest schema parse	✓	395 classes, 13,570 fields
Field-type classification	✓	100% over rac_basic_sample_family 11-release corpus — CI regression gate
Cross-release tag-drift table	✓	First public 122×11 dataset
Layer 5a ADocument walker	partial	Reliable on Revit 2024–2026; 2016–2023 entry-point detection pending
Stream-level modifying writer	✓	13/13 streams byte-preserving; rvt-write CLI + JSON patch manifests
Field-level semantic writer	pending	Phase 7
Layer 5b per-class decoders	✓	80 decoders registered in elements::all_decoders(): Level/Category/Subcategory/Material/FillPattern/LinePattern/LineStyle/BasePoint/SurveyPoint/ProjectPosition/Grid/GridType/ReferencePlane/Wall/WallType/Floor/FloorType/Roof/RoofType/Ceiling/CeilingType/Door/Window/Column/StructuralColumn/Beam/StructuralFraming/Stair/StairType/Railing/RailingType/Room/Area/Space/Furniture/FurnitureSystem/Casework/Rebar/Foundation/Mass/GenericModel/View/Sheet/Schedule/ScheduleView/Titleblock/Viewport/Dimension/TextNote/Tag/Annotation/Revision/Phase/DesignOption/Workset/ParameterElement/SharedParameter/Symbol and every Electrical*/Mechanical*/Plumbing*/Specialty FamilyInstance subtype. Each decoder takes instance bytes → typed view. Validated on synthesized schema+bytes fixtures; real-project-file corpus validation is Q-01.
IFC4 STEP export — spatial tree	✓	IfcProject + IfcSite + IfcBuilding + IfcBuildingStorey + OmniClass classifications
IFC4 STEP export — elements	✓	IfcWall/IfcSlab/IfcRoof/IfcCovering/IfcDoor/IfcWindow/IfcColumn/IfcBeam/IfcStair/IfcRailing/IfcFurniture/IfcFooting/IfcReinforcingBar/IfcSpace/IfcBuildingElementProxy constructors + IfcLocalPlacement + IfcRelContainedInSpatialStructure. Each element is valid IFC4 and appears in BlenderBIM / IfcOpenShell spatial browsers.
IFC4 STEP export — geometry	✓ (rectangular)	IfcExtrudedAreaSolid + IfcRectangleProfileDef chain wired to the element's Representation slot. Rectangular profiles only (curved doors, non-orthogonal walls still pending — IFC-17/24).
IFC4 STEP export — materials	✓	Single-material via IfcMaterial + IfcRelAssociatesMaterial; compound assemblies via IfcMaterialLayerSet + IfcMaterialLayerSetUsage (IFC-28/29). Walls / floors / roofs with layered composition emit correctly.
IFC4 STEP export — properties	✓	IfcPropertySet + IfcPropertySingleValue with typed values (IfcText, IfcInteger, IfcReal, IfcBoolean, IfcLengthMeasure, IfcPlaneAngleMeasure, IfcAreaMeasure, IfcVolumeMeasure, IfcCountMeasure, IfcTimeMeasure, IfcMassMeasure) wired via IfcRelDefinesByProperties.
IFC4 STEP export — openings	✓	IfcOpeningElement + IfcRelVoidsElement + IfcRelFillsElement — doors and windows cut actual holes in their host walls (BlenderBIM verified).
Geometry extraction	partial	Extrusion helpers ship for walls/slabs/roofs/ceilings/columns/beams/stairs/doors/windows (GEO-27..35, IFC-16..26). Swept / revolved / BRep variants exist (IFC-17/18/19/20) but with rvt feature-flagged rectangular fallbacks in the default emission path.
glTF 2.0 binary export	✓	model_to_glb() produces a valid .glb file that loads in Three.js's GLTFLoader (VW1-04). rvt-gltf CLI.
2D plan-view SVG export	✓	render_plan_svg() produces per-category-coloured SVG (walls black, doors blue, columns red, …) (VW1-11). rvt-sheet CLI.
Browser viewer	✓	Live at https://drunkonjava.github.io/rvt-rs/. WebAssembly build of the core library + Three.js + Vite. Zero-upload, in-tab parse, Export glTF/IFC/SVG buttons, URL-based share via share::ViewerState. (VW1-01 through VW1-24 shipped.)
Fuzz-regression harness	✓	9 libFuzzer targets + 38 synthetic adversarial regression cases under tests/fuzz_regressions.rs. Caught a real gzip_header_len bounds bug on 9-byte truncated headers (Q-04).

Why the schema matters

The openBIM community — anchored by buildingSMART International and the IFC standard — has spent years working on Revit interoperability. Autodesk's own revit-ifc exporter runs inside Revit using the Revit API, so it can only emit what the API surfaces. Real-world IFC exports from Revit are described, routinely and publicly, as "very limited" (thinkmoult.com), "data loss" (Reddit r/bim), and "out of the box, just crap" (the OSArch Wiki's guide to Revit for openBIM).

The schema work here — decoding Formats/Latest and classifying 100% of field encodings across 11 Revit releases — is the dictionary a byte-level reader needs. Once per-element decoders (Phase 4 in TODO) and geometry extraction (Phase 5) land on top, the resulting IFC export can carry more than what the Revit API chooses to expose. That is the thesis. It is not yet the delivered product.

If you're building BIM/AEC tooling and want an Apache-2 Revit reader to compose into your stack, the current release covers metadata, schema introspection, 80 per-class decoders (Level, Wall, Floor, Roof, Ceiling, Door, Window, Column, Beam, Stair, Railing, Room, Furniture, Rebar, Phase, DesignOption, Workset, and every Electrical/Mechanical/Plumbing FamilyInstance subtype), and IFC4 STEP emission with a real spatial tree + per-element entities + glTF 2.0 binary + 2D plan-view SVG. See tests/fixtures/synthetic-project.ifc for a committed sample output you can open in BlenderBIM or IfcOpenShell — IfcProject, IfcSite, IfcBuilding, three IfcBuildingStoreys (Ground / Second / Roof Deck at real elevations), and ten IfcWall / IfcSlab / IfcDoor / IfcWindow / IfcStair / IfcBuildingElementProxy entities all wired to the storey via IfcRelContainedInSpatialStructure. Or just drop your file at https://drunkonjava.github.io/rvt-rs/ and click Export IFC — same code path, running in your browser.

Quick demo

One command produces the full forensic picture — identity, upgrade history, format anchors, schema table, Phase D link histogram, content metadata, and a disclosure scan:

cargo build --release
./target/release/rvt-analyze --redact path/to/your.rfa

From Python

import rvt

f = rvt.RevitFile("my-project.rfa")
print(f.version, f.part_atom_title)      # 2024 "0610 x 0915mm"
print(f.read_adocument()["fields"][-1])  # {name: m_devBranchInfo, kind: element_id, tag: 0, id: 35}
open("out.ifc", "w").write(f.write_ifc())

Install: pip install rvt — or build from source with maturin build --release --manifest-path rvt-py/Cargo.toml. Full API + Jupyter notebook walkthrough: docs/python.md and docs/rvt-python-quickstart.ipynb.

In the browser

Drop a .rvt / .rfa / .rte / .rft at https://drunkonjava.github.io/rvt-rs/ — nothing leaves the tab. The viewer compiles the core library to WebAssembly (wasm-pack build --target web --features wasm), runs the parse in a dedicated worker, and renders 3D via Three.js. One-click buttons export the model as glTF 2.0 binary, IFC4 STEP, or plan-view SVG. URL state (camera pose + category filters) is shareable via the hash fragment.

Privacy posture is CI-enforced: the deploy workflow (.github/workflows/deploy-viewer.yml) runs wasm-objdump -j Import on every build and fails if the compiled .wasm imports fetch, XMLHttpRequest, or WebSocket. See docs/viewer-privacy-posture.md.

Sample output (all pre-scrubbed with --redact, committed for review):

• One-screen teaser: docs/demo/rvt-analyze-2024-teaser.txt — the four highlight sections fit in one terminal screen (identity, format anchors, Phase D linkage, disclosure scan)
• Full terminal report: docs/demo/rvt-analyze-2024-redacted.txt — 130 lines of structured output
• JSON report: docs/demo/rvt-analyze-2024-redacted.json — machine-readable version
• Tag-drift heatmap: docs/data/tag-drift-heatmap.svg — visual proof of class-ID drift across 11 Revit releases

The --redact flag (on by default in every committed artifact) scrubs Windows usernames, Autodesk-internal paths, and project-ID folder names to <redacted> markers while preserving path shape so claims remain verifiable. Omit the flag when running privately against your own files.

Results at a glance

Running the shipped CLIs against one 400 KB RFA fixture:

• Metadata: version, build tag, creator path, file GUID, locale (rvt-info)
• Atom XML: title, OmniClass code, taxonomies (rvt-info parses PartAtom)
• Preview: clean PNG thumbnail, 300-byte Revit wrapper stripped (rvt-info --extract-preview)
• Schema: 395 classes + 1,114 fields + per-field typed encoding (rvt-schema)
• History: every Revit release that ever saved this file (rvt-history)
• Bulk strings: 3,746 length-prefixed UTF-16LE records from Partitions/NN — Autodesk unit/spec/parameter-group identifiers, OmniClass + Uniformat codes, Revit category labels, localized format strings (rvt-history --partitions)

Every class and field name that rvt-schema extracts was cross-checked against the public RevitAPI.dll NuGet package's exported C++ symbol list. All top-level tagged class names we've inspected (ADocument, DBView, HostObj, LoadBCBase, Symbol, APIAppInfo, APropertyDouble3, ElementId, and the rest) appear in that export with their decorated signatures (e.g. __cdecl NotNull<class ADocument *,void>::NotNull(class ADocument *)), confirming the on-disk schema names match the compiled symbols one-to-one.

A build-server path also appears in C++ assertion strings inside the same DLL; it is mentioned in the recon report for completeness and does not represent anything the reader extracts from .rvt / .rfa files.

Phase D findings (what makes this project different)

Six reproducible discoveries, all documented in docs/rvt-moat-break-reconnaissance.md and reproducible from examples/:

1. The schema indexes the data. Class names do not appear as ASCII in Global/Latest; class tags from Formats/Latest (u16 after class name, with 0x8000 flag set) occur ~340× the uniform-random rate. The top tag, AbsCurveGStep, appears 19,415 times in 938 KB of decompressed Global/Latest. [examples/link_schema.rs]

2. Tags drift across releases but are stable-sort-assigned. ADocWarnings = 0x001b 2016→2026 because no class sorted alphabetically before it has ever been added. AbsCurveGStep shifted 0x0053 → 0x0066 across the decade as 19 new A-class entries were inserted. Full 122-class × 11-release drift table: docs/data/tag-drift-2016-2026.csv, visualised in docs/data/tag-drift-heatmap.svg. First publicly-available version of this data. [examples/tag_drift.rs]

3. Revit 2021 was a major undocumented format transition. Global/Latest grew 27× (~26 KB → ~715 KB) while simultaneously the Forge Design Data Schema namespaces (autodesk.unit.*, autodesk.spec.*) debuted in Partitions/NN. Two symptoms, one event. Any reader built for 2016-2020 silently drops 30× more data when pointed at 2021+.

4. Parameter-group namespace shipped separately in Revit 2024. autodesk.parameter.group.* identifiers appear in 2024+ only — three releases after units/specs. Dating the Forge schema rollout from on-disk bytes: examples/tag_drift.rs, src/object_graph.rs.

5. A stable Revit format-identifier GUID in family files. Global/PartitionTable is 167 bytes decompressed in .rfa family files, and 165 of those bytes are byte-for-byte identical across every Revit release 2016-2026 (98.8% invariant). The invariant region contains a never-before-published UUIDv1: 3529342d-e51e-11d4-92d8-0000863f27ad. The MAC suffix 0000863f27ad matches a known Autodesk-dev-workstation signature from circa 2000. Useful for family-file detection. Scope correction (2026-04-21): this invariant is a family-file anchor, not a universal Revit-file anchor. Three real .rvt project files we probed carry three different GUIDs (6a6261fd-... on Revit 2023, 552368c6-... on 2024, all-zero on 2025) in a shorter 87-byte PartitionTable. File-type sniffers using the family GUID will correctly reject non-family files but can't identify them. See docs/project-file-corpus-probe-2026-04-21.md. [examples/partition_full.rs]

6. Tagged class record structure decoded. Every class declaration in Formats/Latest carries an explicit tag (u16 with 0x8000 flag), optional parent class, and declared field count, followed by N field records each with name + C++ type encoding. HostObjAttr now resolves to {tag=107, parent=Symbol, declared_field_count=3} with all three field names (m_symbolInfo, m_renderStyleId, m_previewElemId) extracted byte-for-byte. [examples/record_framing.rs, src/formats.rs]

Three unintended disclosure patterns also surfaced in Autodesk's shipped reference content — the specific values are withheld from this README to avoid re-broadcasting them; they are documented in docs/rvt-moat-break-reconnaissance.md for security-research reproducibility:

• A customer-facing OneDrive path that leaks the directory structure of an Autodesk employee's personal sample-authoring workflow.
• A build-server path baked into C++ assertion strings inside the public RevitAPI.dll.
• A creator-name field inside the Contents stream that travels with every copy of the sample family, preserving the name of one of Revit's original 1997 developers.

Downstream safety: the rvt-analyze CLI ships with a --redact flag (on by default for any of the committed demo output in this repo) that rewrites creator paths, Autodesk-internal paths, and build-server paths to <redacted> markers while preserving the surrounding structure. Any tool consuming rvt-rs output and displaying it publicly should do the same.

---

Library surface

All modules compile under both the default build and the wasm feature flag. See src/ for type docs:

Module	What it does
reader	Open any Revit file with OpenLimits, enumerate every OLE stream, fetch raw stream bytes, bounded reads
compression	Truncated-gzip decode (inflate_at, inflate_at_auto, inflate_at_with_limits) + multi-chunk (inflate_all_chunks_with_limits) + truncated-gzip encoder for write-back (truncated_gzip_encode)
basic_file_info	Version, build tag, GUID, creator path, locale — read path + byte-back encoder (BasicFileInfo::encode)
part_atom	Atom XML with Autodesk partatom namespace — title, OmniClass, taxonomies — read + encode
formats	Parse + encode Formats/Latest with FieldType classification (100 % over the 11-release corpus)
walker	Schema-directed instance walker + 80-decoder dispatch + detect_adocument_start entry-point finder
elements	80 ElementDecoder implementations (Wall, Floor, Door, Window, Column, Beam, Stair, Railing, Rebar, Room, Furniture, …)
geometry	Curve / Face / Solid variants (Line, Arc, Ellipse, NURBS, Hermite, Ruled, Revolved, Extrusion, Sweep, Blend, SweptBlend, Boolean, Mesh, PointCloud)
object_graph	DocumentHistory, string-record extractor for Global/Latest + Partitions/NN
class_index	Quick class-name inventory (BTreeSet)
corpus	Cross-version byte-delta classifier
elem_table	Global/ElemTable header parser + rough record enumeration
partitions	Partitions/NN 44-byte header decoder + gzip-chunk splitter
writer	Byte-preserving round-trip copy_file + write_with_patches (atomic temp-file rename, stream-hash verification) + GUID + history preservation
round_trip	Per-class encoder round-trip verification (verify_instance_round_trip)
ifc	Full IFC4 spatial tree + elements + materials + properties + openings + extrusion geometry + glTF 2.0 binary (gltf::model_to_glb) + plan-view SVG (sheet::render_plan_svg) + viewer data model (scene_graph, camera, clipping, sheet, share, measure, annotation, pbr)
streams	Named constants for every invariant OLE stream in a Revit file
redact	Shared PII scrubbers for all CLIs (--redact flag)
wasm	#[cfg(feature = "wasm")] — 14 JS-callable wasm-bindgen bindings powering the browser viewer
error	Structured error type (Error / Result)

Runtime capabilities:

• Open any Revit file from disk (magic D0 CF 11 E0 A1 B1 1A E1)
• Enumerate every OLE stream; find the version-specific Partitions/NN
• Decompress any stream (truncated-gzip format — standard gzip header, no trailing CRC/ISIZE)
• Parse BasicFileInfo, PartAtom, extract preview PNG
• Extract 395 class records from Formats/Latest with tag + parent + ancestor-tag + declared field count for every tagged class
• Decode the 167-byte Global/PartitionTable structure including the stable Revit format-identifier GUID
• Decode the 307-byte Contents stream including the embedded UTF-16LE metadata chunk
• Produce a byte-for-byte round-trip copy of any .rfa / .rvt file
• Run across the full 11-release corpus in < 500 ms per file (release build)

Thirteen CLIs ship in the box:

cargo build --release

# One-shot forensic analysis — all subsystems in one report
./target/release/rvt-analyze --redact my-project.rvt
./target/release/rvt-analyze --redact --json my-project.rvt > report.json

# Quick metadata + schema summary
./target/release/rvt-info --show-classes my-project.rvt

# Machine-readable (JSON)
./target/release/rvt-info -f json my-project.rvt > meta.json

# Pull the embedded thumbnail
./target/release/rvt-info --extract-preview preview.png my-project.rvt

# Compare two versions of the same file (cross-version byte diff)
./target/release/rvt-diff --decompress 2018.rfa 2024.rfa

# Dump the full class schema (395 classes, 13,570 fields)
./target/release/rvt-schema my-project.rvt

# Document upgrade history (which Revit releases have opened this file)
./target/release/rvt-history my-project.rvt

# Pull every UTF-16LE string record out of Partitions/NN
# (categories, OmniClass, Uniformat, Autodesk unit identifiers, …)
./target/release/rvt-history --partitions my-project.rvt

# Hex-dump every decompressed stream (for Phase D work)
./target/release/rvt-dump my-project.rvt

# IFC4 STEP export — spatial tree + elements + geometry + openings
./target/release/rvt-ifc my-project.rvt -o out.ifc

# glTF 2.0 binary export — loads in Three.js / Blender / any glTF viewer
./target/release/rvt-gltf my-project.rvt -o out.glb

# 2D plan-view SVG — per-category colours, ready for plot/laser-cut/printing
./target/release/rvt-sheet my-project.rvt -o out.svg

# Global/ElemTable dump — declared element-ids + record layout (family 12B / project 28B/40B)
./target/release/rvt-elem-table my-project.rvt --limit 20

# Byte-preserving write path — patch stream bytes via JSON manifest
./target/release/rvt-write my-project.rvt --patches patches.json -o patched.rvt

# Per-file doc generator (schema + sample-data render for any RVT)
./target/release/rvt-doc my-project.rvt -o doc.md

# Cross-version corpus analysis (11 releases in one pass)
./target/release/rvt-corpus /path/to/corpus-dir

Thirty-six reproducible probes live in examples/ — one per FACT in the recon report:

cargo build --release --examples

# --- schema ↔ data linkage (Phase D) ---
./target/release/examples/probe_link              <file>           # null-hypothesis: class names absent from Global/Latest
./target/release/examples/tag_bytes               <file>           # hex around known class names in Formats/Latest
./target/release/examples/tag_dump                <file>           # statistical sweep of post-name u16 patterns
./target/release/examples/link_schema             <file>           # tag-frequency histogram in Global/Latest (340× non-uniformity)
./target/release/examples/tag_drift               <sample-dir> <out.csv>   # per-class drift table 2016-2026
./target/release/examples/tag_drift_svg           <in.csv> <out.svg>       # render drift table as colour-coded SVG heatmap

# --- record framing (Phase 4c) ---
./target/release/examples/record_framing          <file>           # dump bytes at tagged-class defs + first tag occurrence
./target/release/examples/elem_table_probe        <sample-dir>     # Global/ElemTable structural sweep across releases
./target/release/examples/partitions_header_probe <sample-dir>     # 44-byte Partitions/NN header + chunk offsets
./target/release/examples/contents_probe          <file>           # Contents stream decoder (creator name + build tag)

# --- stable anchors ---
./target/release/examples/partition_invariant     <sample-dir>     # find 165-byte invariant in Global/PartitionTable
./target/release/examples/partition_diff          <sample-dir>     # show the 2 varying bytes per release
./target/release/examples/partition_full          <file>           # full annotated hex dump + UUID decode

# --- write path (Phase 6) ---
./target/release/examples/roundtrip                                # copy 2024 sample, verify all 13 streams identical

Format overview

Every Revit file is a Microsoft Compound File Binary (OLE2) container with this stream layout (constant across 11 years of Revit releases):

<root>
├── BasicFileInfo                 UTF-16LE metadata
├── Contents                      custom 4-byte header + DEFLATE body
├── Formats/Latest                DEFLATE — class schema inventory
├── Global/
│   ├── ContentDocuments          tiny document list
│   ├── DocumentIncrementTable    DEFLATE — change tracking
│   ├── ElemTable                 DEFLATE — element ID index
│   ├── History                   DEFLATE — edit history (GUIDs)
│   ├── Latest                    DEFLATE — current object state (17:1 ratio)
│   └── PartitionTable            DEFLATE — partition metadata
├── PartAtom                      plain XML (Atom + Autodesk partatom namespace)
├── Partitions/NN                 bulk data: 5-10 concatenated DEFLATE segments
│                                 NN = 58, 60-69 for Revit 2016-2026
├── RevitPreview4.0               custom header + PNG thumbnail
└── TransmissionData              UTF-16LE transmission metadata

All compressed streams use a "truncated gzip" format — the standard 10-byte gzip header (magic 1F 8B 08 ...) followed by raw DEFLATE, but without the trailing 8-byte CRC32 + ISIZE that conforming gzip writers produce. Python's gzip.GzipFile and Rust's flate2::read::GzDecoder both refuse these streams. The fix is to skip the 10-byte header manually and use flate2::read::DeflateDecoder on the raw body.

Reverse engineering state

Layer	Description	Status
1 · Container	OLE2 / Microsoft Compound File ([MS-CFB])	Done
2 · Compression	Truncated gzip → raw DEFLATE	Done
3 · Stream framing	Per-stream custom headers, Partitions/NN chunk layout, Contents / Preview / PartitionTable wrappers	Done — 165/167 bytes of PartitionTable invariant; 44-byte Partitions/NN header decoded; 62 19 22 05 wrapper magic confirmed on Contents + RevitPreview4.0
4a · Schema table	Class names + fields + C++ type signatures from Formats/Latest; per-class tag + parent + declared field count; cross-release tag-drift map	Done
4b · Schema→data link	Tags from Formats/Latest occur at ~340× the noise rate in Global/Latest; schema IS the live type dictionary for the object graph	Done
4c.1 · Record framing	Tagged class records in Formats/Latest parse into structured records: {tag, parent, ancestor_tag, declared_field_count}; HostObjAttr → {tag=107, parent=Symbol, ancestor_tag=0x0025 → APIVSTAMacroElem, declared_field_count=3}	Done
4c.2 · Field-body decoding	FieldType enum classifies 100% of schema fields across 8 variants (Primitive, String, Guid, ElementId, ElementIdRef, Pointer, Vector, Container). 11 discriminator bytes mapped, including generalized scalar-base Vector/Container ({kind} 0x10 ... / {kind} 0x50 ...) and the 0x0d point-type base.	Done (100.00% on 13,570 fields across the 11-version corpus; zero Unknown)
4d · ElemTable	Global/ElemTable header parser + rough record enumeration; record semantics TBD (blocked on per-element schema lookup)	Partial
5 · IFC4 export	Full spatial tree + per-element IFC entities + IfcLocalPlacement + IfcExtrudedAreaSolid + compound material layers + typed property sets + IfcOpeningElement/IfcRelVoidsElement/IfcRelFillsElement for doors and windows. Deterministic ISO-10303-21 output. IfcOpenShell + BlenderBIM verified.	Done (rectangular profiles; swept / revolved / BRep fallbacks ship but use rectangular in the default emission path — IFC-17/24 is the remaining refinement)
6 · Write path	Byte-preserving read-modify-write round-trip (13/13 streams identical); rvt-write CLI + JSON patch manifest + atomic temp-file rename + per-stream SHA verification (WRT-11..14). Stream-level patch is end-to-end; field-level semantic patching is Phase 7.	Done (stream-level); field-level pending
7 · Browser viewer	WebAssembly build of the core + Three.js + Vite + Pages deploy. Zero-upload, in-tab parse, export buttons for glTF/IFC/SVG, URL-state share. Live at https://drunkonjava.github.io/rvt-rs/.	Done (VW1-01..24)

All 5 original P0 research questions (Q4-Q7) are resolved. Layer 4c.2 reaches 100.00% field-type classification on the 11-version reference corpus (13,570 total schema fields, zero Unknown). IFC4 emission, glTF export, 2D plan view, and the browser viewer all ship. The next frontier is real-world project-file corpus validation (Q-01) — one .rvt probe already caught a gzip_header_len bounds bug that family files never hit.

Key findings from this phase:

• Q4 The u16 "flag" word in each tagged-class preamble is a class-tag reference (ancestor / mixin / protocol). 9/9 non-zero values resolve to named classes in the same schema.
• Q5 Each field's type_encoding is [byte category][u16 sub_type][optional body]. 9 category bytes mapped (0x01 bool, 0x02 u16, 0x04/0x05 u32, 0x06 f32, 0x07 f64, 0x08 string, 0x09 GUID, 0x0b u64, 0x0e reference/container).
• Q5.1 Coverage extended to 84% of fields.
• Q5.2 Coverage reaches 100% of fields (13,570 across 11 releases). Generalized {scalar_base} 0x10 ... / {scalar_base} 0x50 ... as vector/container modifiers; added 0x0d point-type base; added 0x08 0x60 ... alternate string encoding; added ElementIdRef { referenced_tag, sub } for references that carry a specific target-class tag; added deprecated 0x03 i32-alias seen only in 2016–2018. See docs/rvt-moat-break-reconnaissance.md §Q5.2.
• Q6 Global/Latest is not an index + heap — it's a flat TLV stream.
• Q6.1 Instance data is schema-directed (tag-less, protobuf-style). Decoding requires schema-first sequential walk from a known entry point.
• Q7 Partitions/NN trailer u32 fields are not per-chunk offsets. Gzip-magic scan remains correct.

The full analysis narrative with 12 dated addenda lives in docs/rvt-moat-break-reconnaissance.md. Session-length synthesis in docs/rvt-phase4c-session-2026-04-19.md.

Sample corpus

Integration tests run against 11 versions of Autodesk's public rac_basic_sample_family RFA fixture (one per Revit release from 2016 through 2026). These are distributed via Git LFS in the phi-ag/rvt repository. To pull them:

cd /path/to/rvt-recon/samples
git clone https://github.com/phi-ag/rvt.git _phiag
cd _phiag && git lfs pull
cd .. && cp _phiag/examples/Autodesk/*.rfa .

The integration tests in tests/samples.rs skip any year whose RFA file is absent, so partial corpora are okay — you'll just see skipping 2024: sample not present messages.

Design choices

• cfb crate over custom OLE parser — the cfb crate is mature, tested against Office documents, and handles both short and regular sectors. Faster than writing our own.
• flate2 over miniz_oxide direct — flate2 wraps both miniz_oxide (pure Rust) and libz backends. We pick the default pure-Rust build to avoid a C toolchain dependency.
• quick-xml over xml-rs — ~3x faster, zero-copy friendly, and the .from_str + event-loop pattern is closer to what Go/Python parsers do.
• encoding_rs over stdlib — Revit's UTF-16LE streams sometimes have malformed pairs at boundaries (single-byte markers get interleaved). encoding_rs recovers gracefully where stdlib panics.
• BTreeSet for class names — deterministic ordering in output (plus sorted JSON) matters for diffable CLI output.

Running the tests

cargo test --release

Expected output (as of 2026-04-21):

test result: ok. 697 passed; 0 failed   (lib unit tests)
test result: ok.  38 passed; 0 failed   (fuzz-regression harness, Q-04)
test result: ok.   9 passed; 0 failed   (integration tests, 11-version corpus)
test result: ok.   3 passed; 0 failed   (ifc_roundtrip + ifc_synthetic_project/structural)
...

Integration tests are skipped if the sample RFAs are absent. The fuzz-regression harness (tests/fuzz_regressions.rs) runs hand-crafted adversarial inputs through each libFuzzer target's entry point — no libFuzzer runtime needed — so any future commit that regresses crash-resistance trips the gate locally.

License and trademarks

• Code: Apache License 2.0. See LICENSE for the full text and NOTICE for attribution detail.
• Trademarks: "Autodesk" and "Revit" are registered trademarks of Autodesk, Inc. This project is not affiliated with, endorsed by, or sponsored by Autodesk. References to "Autodesk" and "Revit" in this project identify the file format this reader parses and are nominative fair use.
• Interoperability basis: reverse engineering for the purpose of creating an independently-developed interoperable program is recognised as lawful fair use under Sega Enterprises v. Accolade, 977 F.2d 1510 (9th Cir. 1992) and Sony Computer Entertainment v. Connectix, 203 F.3d 596 (9th Cir. 2000) in the United States, and under Article 6 of the EU Software Directive 2009/24/EC in the European Union. File formats themselves are not copyrightable subject matter (Baker v. Selden, 101 U.S. 99 (1879); Lotus Development v. Borland, 516 U.S. 233 (1996)).
• No Autodesk proprietary code is used, referenced, or redistributed by this project. All file-format observations were made by inspecting the bytes of publicly-shipped Autodesk sample content and by parsing the public RevitAPI.dll NuGet package's exported symbol list. See NOTICE.